1. Field of the Invention
The present invention relates to an image forming apparatus that has a tab-inserting function of delivering a bundle of recording sheets with tab sheets inserted therein.
2. Description of the Related Art
Conventionally, image forming apparatuses, such as copying machines and printers, are provided with a plurality of feed trays, and are capable of forming images on sheets having different sizes and outputting the same. Further, the feed trays include a front-loading tray which is disposed in the body of the image forming apparatus and pulled out toward the user to set sheets therein, a deck which is disposed outside the body of the apparatus and capable of containing a large number of sheets, and a multi tray which is capable of having irregularly-sized sheets set therein.
Further, a sheet fed from the front-loading tray is conveyed via a U-shaped conveying path to an image transfer position, and therefore an image is transferred onto the lower surface of the sheet. On the other hand, a sheet fed from the deck or the multi tray is linearly supplied to the image transfer position, and therefore an image is transferred onto the upper surface of the sheet. That is, whether an image is transferred onto the upper surface of a sheet or the lower surface of a sheet depends on a path via which the sheet is fed.
Further, these feed trays can have stacked thereon not only plain paper, but also various types of materials, such as thick paper, OHP sheets, glossy paper, and envelopes. Tab sheets are among them. The tab sheets are formed with tabs for division of sheets, and a bundle of table sheets is comprised of a plurality of tab sheets arranged such that the respective locations of tabs on the tab sheets are sequentially shifted from an uppermost location to a lowermost location. For example, there are three-tab sheets formed by three sheets each formed with a tab, and five-tab sheets formed by five sheets each formed with a tab. One set of three-tab sheets is comprised of three tab sheets, and one set of five-tab sheets is comprised of five tab sheets. In general, the tab sheets forming one set are sequentially named a first page, a second page, a third page, . . . , starting with a sheet formed with a tab at the uppermost location.
On the other hand, the image forming apparatus is also provided with a plurality of discharge trays for discharging sheets. Particularly, for a multifunction machine, which has a copying function, a printing function, a facsimile function, and so forth, integrated in a single unit, it is an essential requirement to have a plurality of discharge trays for sorting sheets discharged by these functions.
The discharge trays are largely classified into a face-up tray onto which sheets are discharged with an image-transferred surface thereof facing upward, and a face-down tray onto which sheets are discharged with an image-transferred surface thereof facing downward.
Trays often used in conventional copying machines, which allow sheets to be linearly discharged out in a conveying direction, are examples of the face-up tray, and trays often used in conventional printers, which are disposed at the top of the printers and allows sheets to be discharged, are examples of the face-down tray.
When a bundle of sheets are discharged onto the face-up tray or the face-down tray, since a new sheet is stacked on sheets already stacked on the discharge tray, the order of output of pages is different between the face-up tray and the face-down tray. Normally, onto the face-up tray, sheets are discharged starting with the last page first, whereas onto the face-down tray, sheets are discharged starting with the first page first.
To this end, depending on the type of discharge trays onto which sheets are to be discharged, control is provided such that the order of pages to be output is switched over. Further, some image forming apparatuses are capable of inverting sheets printed with images during conveyance thereof inside the machine, to use a face-up tray as a face-down tray.
Further, as for tab sheets, even when they are discharged onto the face-up tray, they are discharged starting with the first page of a tab sheet bundle, so that the order of tabs in the tab sheet bundle discharged onto the face-up tray is reversed. To eliminate this inconvenience, some commercially available tab sheets are provided, which are already reversed in the order of pages of a tab sheet bundle. A bundle of tab sheets stacked in a normal page order is called a normal tab sheet bundle. The first page of the normal tab sheet bundle has a tab formed at an uppermost location of a right-hand side thereof, and the following pages each have a tab formed at a lower location than the location of a tab on the immediately preceding page. A bundle of tab sheets stacked in a reverse page order is called a reverse tab sheet bundle. The last page of the reverse tab sheet bundle has a tab formed at an uppermost location of a right-hand side thereof, and the preceding pages each have a tab formed at a lower location than the location of a tab on the immediately following page.
The conventional image forming apparatuses are constructed as described above, and therefore, to print on tab sheets, if they are to be discharged onto the face-up tray, it is only necessary to use a reverse tab sheet bundle, whereas if they are to be discharged onto the face-down tray, it is only necessary to use a normal tab sheet bundle.
This did not raise any problems insofar as sheets could be fed only from trays that contain sheets to be conveyed to the image transfer position without being inverted or made upside down. With the progress of the sheet conveying technique, however, it has become technically possible to convey any type of material, and tab sheets can be also conveyed even from front-loading trays from which sheets are fed to be inverted during conveyance, causing the page order of the tab sheets to be reversed. Therefore, when users want to print on tab sheets, it is necessary to set a suitable type of tab sheets in a feed tray, after considering whether the sheets are inverted in the conveying path from the feed tray to the image transfer position, or in the conveying path from the image transfer position to a discharge tray. This increases the operating burden on the users, and there is a fear of producing a heap of misprints, before tab sheets are discharged as desired, which raises a problem in operating the conventional image forming apparatuses.